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| Illustration 1 | g06140728 |
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Hoist Control Valve in the HOLD position (3) Hoist Control Valve (3A) Pilot Control Actuator (3B) Pilot Control Actuator (3C) Valve Spool (3D) Relief Valve (3E) Check Valve (3F) Spring (3G) Spring (A) Raise Port (B) Load Sensing Port (C) Lower Port (D) Tank Port (E) Pump Port | |
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| Illustration 2 | g06140705 |
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The hoist control valve is on the left side rear of the tractor. (3) Hoist Control Valve (3A) Pilot Control Actuator (3B) Pilot Control Actuator (3D) Relief Valve (3E) Check Valve (A) Raise Port (B) Load Sensing Port (C) Lower Port (D) Tank Port (E) Pump Port | |
The position of valve spool (3C) is determined by the magnitude of the pilot pressure within pilot control actuators (3A) and (3B). This pilot pressure, that acts on the Valve spool, is controlled by the solenoids that are part of the pilot control actuators. The solenoids are connected to the hoist control, which is in the cab, via the ECM. The valve spool has four positions.
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| Illustration 3 | g03471043 |
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Valve spool in the Hold position | |
When the engine is shut off or the engine is running, the magnitude of the pilot pressure within pilot control actuators (3A) and (3B) is zero. The valve spool is centered to the HOLD position by springs (3F) and (3G). Oil flow from the piston pumps is blocked at pump port (E).
Since there is no load sensing pressure through load sensing port (B) and no demand on the hoist system the piston pump will be at the minimum swashplate angle but the piston pumps will maintain a standby pressure.
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| Illustration 4 | g03474997 |
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Valve spool in the Raise position | |
When the hoist control is moved to the RAISE, the ECM sends a current to pilot control actuator (3A), which is proportional to the displacement of the hoist control in the cab. Pilot control actuator (3A) is energized. The pilot pressure within the pilot control actuator moves valve spool (3C) to the RAISE position. Oil within pilot actuator (3B) is directed to the hydraulic tank. The valve spool is moved fully to the right. Oil flows from pump port (E) through check valve (3E) to the piston sides of the hoist cylinders from raise port (A). Oil flows from the rod sides of the hoist cylinders to lower port (C). This oil flows from lower port (C) to tank port (D). The hoist cylinders extend and the body is raised.
At the same time, pressure is felt at load sensing port (B). The load sensing signal is sent to the piston pumps to maintain the demand for the hoist (RAISE).
When the hoist control is moved to the LOWER, the ECM sends a current to pilot control actuator (3B), which is proportional to the displacement of the hoist control in the cab. Pilot control actuator (3B) is energized. The pilot pressure within pilot control actuator (3B) moves valve spool (3C) to the LOWER. Oil within pilot actuator (3A) is directed to the hydraulic tank. The valve spool is moved fully to the left. Oil flows from pump port (E) through check valve (3E) to the rod sides of the hoist cylinders from lower port (C). Oil flows from the piston sides of the hoist cylinders to raise port (A). This oil flows from raise port (A) to tank port (D). The hoist cylinders retract and the body is lowered.
At the same time, pressure is felt at load sensing port (B). The load sensing signal is sent to the piston pumps to maintain the demand for the hoist (LOWER).
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| Illustration 5 | g03475018 |
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Valve spool in the Float position | |
When the hoist control is moved to the FLOAT position, Pilot control actuator (3B) is partially energized. The pilot pressure within pilot control actuator (3B) is moved to the FLOAT. Oil within pilot actuator (3A) is directed to the hydraulic tank. The valve spool is moved partially to the left. Oil flow to pump port (E) is blocked. Raise port (A) and lower port (C) are also connected to tank port (D).
Since there is no load sensing pressure through load sensing port (B) and no demand on the hoist system the piston pump will be at the minimum swashplate angle but the piston pumps will maintain a standby pressure.
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| Illustration 6 | g01027336 |
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(3D) Relief Valve
(3aa) Chamber (3bb) Ball Valve (3cc) Spring (3dd) Passage (3ee) Piston (3ff) passage | |
Relief valve (3D) limits the system pressure when the hoist cylinders retract and the body is lowered.
Pressure inside chamber (3Aa) acts on ball valve (3Bb). When the pressure exceeds the setting on the relief valve, ball valve (3Bb) is moved against spring (3Cc) and the pressure inside chamber (3Aa) is relieved through passage (3Dd). Piston (3Ee) is moved to the right and pressure is relieved to the tank through passage (3Ff).